The present invention is directed to a device to produce molded plastic parts, especially foam parts, using a flowable reaction mixture. The device broadly consists of a molding tool with a mixhead. A sprue runner leads from the outlet of the mixhead to the molding cavity.
To produce molded plastic parts, e.g., molded foam parts, using a flowable reaction mixture which forms a polyurethane or polyurethane foam, a molding tool with a mixhead which is either permanent, or is in place only while the mixture passes through it, is generally used. Most often, ejection piston mixheads are used because of their self-cleaning ability. Other types of mixheads can also be used. No matter which mixhead type is used, when a sprue runner which leads from the outlet of the mixhead to the mold cavity, is used, this sprue runner is contaminated with the remnant of the reaction mixture. The remnant of the reaction mixture contains unmixed or incompletely mixed reaction components. These contaminants must be removed to guarantee the production of high quality molded parts. The cleaning is done either with a compressed air pistol or with solvents. Both methods discharge waste into the environment. The cleaning also unnecessarily prolongs the cycle time for the part production. This lost time adds up to a considerable cost factor in the course of a work shift.
The object of the present invention was to design a device of the type mentioned above, where a contamination of the sprue runner by unmixed or poorly mixed reaction components would be avoided in order to shorten the production cycle of the molded parts by eliminating the cleaning time.